I think it's the track use that is hard on the chain. I've had a number of sport bikes as well, and only the two with sustained track day usage have had loosened cam chains develop over time. Definitely took a couple of years with the ZX-6R, and now with the 3rd year of ZX-10R ownership [maybe 50% track miles], and same issue.

Road bikes that don't get revved as hard - no issues at all.

I do try to match revs when shifting [even on track], and while that helps smoothness on corner entry, it may not have protected the engine as much. That said, despite having high mileage bikes in some cases, I've never grenaded a clutch.....praise beer!